Internal combustion engines typically drive several accessories through a belt arrangement operating off the engine crankshaft. For example, an exemplary modern vehicle engine might drive such accessories as: air pump, alternator, fan, air conditioning compressor, power steering pump and water pump. A well recognized problem with such accessories as conventionally belt driven is that their rate of rotation is proportional to engine speed. Consequently, the designs of the accessories have been subject to substantial compromise in order to insure adequate performance at low engine speeds and dependability and reasonable longevity at high engine speeds. In recognition of these contradictory requirements, it has been proposed that a variable speed accessory drive be employed which would serve to drive the accessories relatively faster at lower engine speeds and relatively slower at higher engine speeds.
If such an effective variable speed accessory drive can be realized, numerous benefits would be obtained. For example: the life of the bearings of such accessories would be greatly extended, power absorption at high speed would be greatly reduced such that more engine net power output would be available, fuel economy would be improved, better accessory performance at low engine speeds (such as idle) would be obtained and smaller accessories could be employed with resulting savings in initial cost and weight.
In the variable speed accessory drives which have been proposed in the past, most have employed V-belt drives in which the driving and/or driven pulley is rendered variable in diameter by axially adjusting (under the influence of some speed responsive control system) the pulley sheave sections in order that the V-belt will ride at various depths in the variable diameter pulley. The fixed positions of the driving and driven pulley axes together with the fixed belt length results in the belt being tensioned and positioned radially in one of the driving or driven pulleys in an inverse fashion to the other of the driving or driven pulleys in a manner well known to the designers of such variable speed drives. Flat belt variable speed accessory drives have also been proposed that offer significant advantages relative to the V-belt drives. In either the flat belt or V-belt variable speed accessory drive systems, there is a major reduction in the complexity and cost by using only one variable diameter pulley and absorbing the required belt takeup with a belt tensioner. It is possible to independently control and change the diameter of the rotating pulley about which the belt passes using the belt tensioner as a dependently operating element--i.e., tensioning the belt by an idler pulley positioned on an arm rotated and acted upon by a spring. However, there are significant problems associated with using an independent control for varying the diameter of a rotating pulley that results in increased weight, complexity and cost. The overall system is rendered lower in weight, complexity and cost by employing the belt tensioner of this invention as the active speed ratio control--the independently operating element--and using as the dependent operating element, the variable diameter pulley involving integral spring and centrifugal weight force components.
A typical variable diameter driving pulley is shown in U.S. Pat. No. 2,310,081 where the centrifugal force of balls is used to change the effective belt radius in a V-belt pulley in order to drive an automobile generator at a more constant speed. The simpler belt takeup tensioner of this invention can replace one of the V-belt pulleys used in U.S. Pat. Nos. 4,216,678, 4,432,743 and 4,639,239, all of which are limited to being passive control systems. Their speed ratios are changed on a predetermined schedule of pulley speed and torque rather than by command as obtained by this invention. However, there are also more complicated and costly active control systems such as shown in U.S. Pat. No. 4,772,248, which uses hydraulic fluid control pressure to act in one V-belt pulley to change the speed ratio with another variable diameter pulley reacting by using a diaphragm spring. U.S. Pat. No. 4,854,921 involves a complicated active control system employing a flat belt driving pulley with a spring operated tensioner. In this invention, a controlled hydraulic pressure changes the accessory to engine speed ratio upon command. Thus, this invention has basic advantages in permitting the design and use of simpler, less costly variable diameter pulleys.
Many patents have been issued for belt tensioners that operate to tension belts passing around fixed diameter pulleys. These patents usually employ spring loaded idler pulleys in various arrangements to tension the belt. Spiral springs are often used to rotate the arm on which an idler pulley is used to tension the belt. Such arrangements are shown in U.S. Pat. No. 4,557,709 to R. C. St. John; in U.S. Pat. No. 4,563,167 to R. C. Foster; and U.S. Pat. No. 4,596,538 to D. D. Henderson. Belleville springs are used in belt tensioning arrangement shown in U.S. Pat. No. 4,151,756 to R. Binder, et al; in U.S. Pat. No. 4,509,935 to R. C. Foster, et al; and in U.S. Pat. No. 4,270,906 to D. H. Kraft and D. M. Rinaldo. Other spring arrangements include helical springs as well as a rubber band spring (U.S. Pat. No. 4,571,223 to E. W. Molloy). Hydraulic pressure is also used to operate other belt tensioners, such as shown in U.S. Pat. No. 4,276,038 to D. H. Kraft or as shown in U.S. Pat. No. 3,142,193 to P. P. Polko et al. Also, U.S. Pat. No. 4,249,425 to R. D. Watson employs a vacuum motor stroked by the engine intake vacuum to tension the belt passing around an idler pulley. All of the above tensioners are basically different from this invention, being passive control systems--not under arbitrary command such as the system of this invention which can operate in incremental steps to change the operating belt radius in an associated pulley. My invention is directed to a variable speed accessory (and supercharger) belt drive which permits a comparatively low cost and low weight system to be obtained employing only one variable diameter pulley with an active tensioner control. The belt shape, depending on the variable diameter pulley, can be flat, V-ribbed, Vee or other cross-section.